SEATTLE -- Four people suspected of being part of a group claiming to have explosives and a sniper inside the old Horace Mann school building were arrested Tuesday, ending a weeks-long standoff between the group and the Seattle School District, according to the Seattle Police Department.

The District closed the school building on East Cherry Street years ago. In recent months, 18 groups moved into the school without permission and started using it for community classes and other purposes as the Africatown Center for Education and Innovation.

But the district is trying to renovate the building to be used as a high school next fall and district officials say the delays are costing the district thousands in construction penalties.

According to police, the district successfully negotiated with most of the groups to leave, but a small number of people remained in the building, refusing to leave and threatening anyone who approached the buildings with explosives and a rooftop sniper.

Once police learned only a few people would be inside the building Tuesday, they swarmed the building with SWAT teams to clear anyone inside and check for any explosives as students at nearby Garfield High sheltered in place.

"Whether it's credible or not, just that it's said by the people occupying the place that's good enough for us out of concern for officers and the community and school nearby we took that threat very seriously," said Renee Witt with Seattle police.

No explosives were found and police arrested the four people inside for investigation of criminal trespassing. Sources say the group's leader Omar Tahir Garrett was among those arrested. Garrett is the same man who was convicted of breaking then Mayor Paul Schell's eye socket with a bullhorn during a rally in July of 2001.

The four were released Tuesday evening but their cases were forwarded to the city prosecutor for review.